This invention relates to control arrangements for deactivatable valves for internal combustion engines.
German Offenlegungsschrifts Nos. 35 19 471 and 37 01 609 and German Patent No. 3 526 542 disclose various arrangements for controlling the operation of deactivatable valves in internal combustion engines. For example, they provide the advantageous possibility of maintaining individual inlet valves closed at low engine speeds and loads so that the change of cylinder gases will take place through only some of the inlet valves. This can improve the after-charge effects because of the corresponding reduction of the cylinder inflow cross-sectional area.
In the designs disclosed in the first two references mentioned above, a single cam on the camshaft is provided for actuating both valves, that is, both a regularly actuated valve and a valve which may be maintained closed or actuated when appropriate. For this purpose, the valve-actuating levers for the two valves can be connected to each other, for example, by hydraulic pressure operating on a coupling arranged between the valve-actuating levers. This pressure produces a relative axial displacement of the bearing portions of the two actuating levers on the shaft so as to bring them into engagement.
The operation of the valve-actuating mechanism according to German Patent No. 3 526 542 is exactly the same in principle, but the coupling is of a configuration such that there is no relative sliding motion between the two actuating levers, and the coupling and release of the two transmission levers from each other is effected by axial motion of a piston which is eccentric to the shaft. Because only small pressure areas are available, this alternative requires high-pressure hydraulics.
Conventional engines are limited to merely activating and deactivating individual valves. Additional enhancements of torque and output of the engine could be achieved if the control times of the valves were also variable as functions of operating parameters of the engine, such as the rotational speed and load. On this point, Germany Offenlegungsschrift No. 37 35 998 discloses a valve-actuating mechanism having three cams on one camshaft and three actuating levers which are also capable of being selectively coupled and released by a piston-and-pin coupling. Since the central cam is designed for a greater travel than the other two cams, in the case of engagement actuating of the coupling described, it controls the displacement of all three valves when their actuation levers are coupled. Otherwise, the displacement of each valve is controlled by the cam individually assigned to it. In other words, this arrangement, while providing the possibility of selecting from several different valve control times, does not permit deactivation of individual valves.